As a Hairdresser in a previous life :) this is one that i have used and that i highly recommend.

Used in conjunction with the fried lice spray it is a godsend.

In my 3rd year of apprenticeship i caught headlice off a teenager! whose mum had sent him into the salon for a haircut, the place i worked at's policy was if you have started the haircut you have to finish, it was something i hated. So i finished the haircut and became riddled with lice, the first time i had ever had them i was devastated. I brought some of this on my way home and ended up sleeping with it in and washing it out the next day.

i always have some of this in my cupboard even though i haven't been a hairdresser for 3 years i'm still a bit paranoid.

It is pricier than some of the other options but it works really well.